[time-nuts] HP 5370a

[paul swed]

Matthias
OK my diagrams show traditional parts like ecl gates. To Bruces comment
that the delay line is not coax. Makes sense. But I have never had to get
to the level you will need. It is odd that two do not work. But
interpolators are funny things and its possible both are on some edge. Not
to mis-lead you.
By the way at this point if I have a piece of test gear thats basically
Dead I dive in and open cans etc. The nothing to loose mode.
Best of luck
Paul
WB8TSL

On Sun, Jul 5, 2015 at 5:13 AM, Matthias Jelen <Matthias.Jelen at gmx.de>
wrote:

> The problem is that the whole VCO is packaged. The connections from the
> VCO to the outside world are fairly simple: -5,2 Volt, a bias for the
> buffer amplifier, the tuning voltage and the start/stop line. The
> start/stop line is tied to gnd with 2.2 µH, so even if the start/stop
> circuit woud fail I can´t see how the oscillator could be kept from
> oscillating permanently.
>
> Anyone successfullly opened such a package (without damaging it
> permanently?)
>
> Regards,
>
> Matthias
>
>
> Am 05.07.2015 um 07:54 schrieb Bruce Griffiths:
>
>> On Saturday, July 04, 2015 05:20:45 PM paul swed wrote:
>>
>>> Matthias
>>> I am afraid I am not much help here.
>>> I did look at the a19/20 interpolators. A lot going on in that small
>>> space.
>>> I guess i would check the 200 MHz feeding into it. The VCO is fairly
>>> simple
>>> in using a gate and a delay line. I will guess the delay line is coax..
>>>
>> No its microstrip within the VCO package. Other coax delays are used in
>> the oscillator turnoff and mixer logic.
>>
>>> But there are all kinds of gates to control the system and Flip Flop used
>>> as a mixer. Not easy to deal with.
>>> Regards
>>> Paul.
>>>
>>> On Sat, Jul 4, 2015 at 1:44 PM, Matthias Jelen <Matthias.Jelen at gmx.de>
>>>
>>> wrote:
>>>
>>>> Dear Time-Nuts,
>>>>
>>>> I´m still struggling to get my 5370A to work reliable again. It keeps
>>>> showing error 04.
>>>>
>>>> Sometimes it is working without any problems for hours, sometimes it
>>>>
>>> ´s a
>>
>>> matter of minutes until the error is displayed, and sometimes I doesn
>>>>
>>> ´t
>>
>>> come up without the error at all. I don´t think it´s related to
>>>> temperarure, the usual procedures with a hairdryer and cooling spray
>>>> didn´t
>>>> show any effects.
>>>>
>>>> I dug into this a bit. It seems like the startable VCO on one of the
>>>> interpolator boards isn´t working reliable anymore. The error stays
>>>>
>>> with
>>
>>> the board, no matter if I put it into the slot for the start channel or
>>>> the
>>>> stop channel. If the unit is in the non-working-state, there is no RF at
>>>> the output of the VCO. As soon the VCO oscilates, the PLL locks and
>>>> everything works fine, only the tuning voltage is a bit outside the
>>>>
>>> range
>>
>>> given in the service manual. If the VCO stops oscillating, the tuning
>>>> voltage runs to it´s lower rail, just as expected. I opened the PLL loop
>>>> and tuned the VCO with a external power supply, this works as
>>>>
>>> expected -
>>
>>> no
>>>> regions in the tuning range in which the oscillator stops working or
>>>> similiar.
>>>>
>>>> I checked the signals going to the board, and they all look OK.
>>>>
>>>> I fooled the logic that detects a tuning voltage outside the allowed
>>>>
>>> area,
>>
>>> and as expected, the error 04 isn´t displayed anymore, but also as
>>>> expected
>>>> the unit still stops working.
>>>>
>>>> I pulled the board, removed some components and supplied power to
>>>>
>>> the VCO
>>
>>> from an external power supply - same behaviour here.
>>>>
>>>> So I came to the conclusion that the VCO itself is defective, although I
>>>> have no idea what could cause a VCO to behave that way.
>>>>
>>>> Now for the strange part: A noble member of this list sent me a spare
>>>> interpolator board which was pulled from a working unit. This shows
>>>> exactly
>>>> the same behaviour! Also at this board the tuning voltage is outside
>>>>
>>> the
>>
>>> given window, and the oscillator doesn´t start from time to time.
>>>>
>>>> If a dead VCO module is a common problem, I´d expect that someone
>>>>
>>> on this
>>
>>> list also experienced this problem before. Otherwise, I think it´s
>>>> unlikely
>>>> that I found two defective interpolator boards in a row. I stil have the
>>>> feeling that I´m overlooking something simple. So `d be happy to
>>>>
>>> receive
>>
>>> any comments on this. Also, if someone wants to get rid of a 5370
>>>>
>>> that
>>
>>> needs repair I might be interested.
>>>>
>>>> I guess this is what you can expect if your´re using test equipment
>>>>
>>> which
>>
>>> was introduced before you were born, but it´s part of the fun...
>>>>
>>>> Thanks,
>>>>
>>>> Matthias
>>>>
>>>>
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